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Publication AbstractsFiber Size, Type, and Myosin Heavy Chain Content in Rhesus Hindlimb Muscles after 2 Weeks at 2 GMorteza Tavakol, Roland R. Roy, Jung A. Kim, Hui Zhong, John A. Hodgson, Tana M. Hoban-Higgins, Charles A. Fuller, and V. Reggie EdgertonAviat Space Environ Med 2002; 73:551-7 AbstractBackground: Fiber atrophy and an increase in the percentage of fast fibers have been observed in Rhesus leg muscles after spaceflight. Hypothesis: Hypergravity will result in muscle fiber hypertrophy and an increase in the percentage of slow fibers. Methods: Open muscle biopsies were obtained from Rhesus soleus, medial gastrocnemius (MG), and tibialis anterior (TA) muscles before and after 14 d of centrifugation (2 G) and in time-matched controls. Cage activity levels were measured by telemetry. Results: Based on monoclonal antibody binding for myosin heavy chains (MHC), the fastest region of soleus contained a higher proportion of type I+II (27 vs. 13%) and had a tendency for a lower proportion of type I (38 vs. 61%, p = 0.10) fibers after than before centrifugation. There was a higher proportion of type I+II fibers in post- vs. pre-2 G (10 vs. 0.6%) MG biopsies. Fiber type distribution and MHC composition were unaffected in the TA. Overall, mean fiber sizes were unaffected by centrifugation. Average cage activity levels were 36% lower during than before 2 G. Conclusions: Our hypothesis was rejected. The changes in the proportion of fibers expressing type I MHC are the reverse of that expected with chronic loading of extensors and, paradoxically, are similar to changes observed with chronic unloading, such as occurs during spaceflight, in this primate model. The data are consistent with the observed decrease in total daily activity levels.Keywords: hypergravity, Rhesus, skeletal muscle plasticity, biopsies, fiber types, myosin heavy chain. Information on subscribing, and on obtaining copies of an article or of an entire issue. Table of Contents for Volume 73, Number 6 of the ASME journal.
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